The present invention relates to computer animation. More particularly, the present invention relates to techniques and apparatus for rendering of more natural-looking wrinkles or creases on a posed object.
Throughout the years, movie makers have often tried to tell stories involving make-believe creatures, far away places, and fantastic things. To do so, they have often relied on animation techniques to bring the make-believe to “life.” Two of the major paths in animation have traditionally included, drawing-based animation techniques and stop motion animation techniques.
Drawing-based animation techniques were refined in the twentieth century, by movie makers such as Walt Disney and used in movies such as “Snow White and the Seven Dwarfs” (1937) and “Fantasia” (1940). This animation technique typically required artists to hand-draw (or paint) animated images onto a transparent media or cels. After painting, each cel would then be captured or recorded onto film as one or more frames in a movie.
Stop motion-based animation techniques typically required the construction of miniature sets, props, and characters. The filmmakers would construct the sets, add props, and position the miniature characters in a pose. After the animator was happy with how everything was arranged, one or more frames of film would be taken of that specific arrangement. Stop motion animation techniques were developed by movie makers such as Willis O'Brien for movies such as “King Kong” (1933). Subsequently, these techniques were refined by animators such as Ray Harryhausen for movies including “Mighty Joe Young” (1948) and Clash Of The Titans (1981).
With the wide-spread availability of computers in the later part of the twentieth century, animators began to rely upon computers to assist in the animation process. This included using computers to facilitate drawing-based animation, for example, by painting images, by generating in-between images (“tweening”), and the like. This also included using computers to augment stop motion animation techniques. For example, physical models could be represented by virtual models in computer memory, and manipulated.
One of the pioneering companies in the computer aided animation (CAA) industry was Pixar. Pixar developed both computing platforms specially designed for CAA, and animation software now known as RenderMan®. RenderMan® was particularly well received in the animation industry and recognized with two Academy Awards®. RenderMan® software is used to convert graphical specifications of objects and convert them into one or more images. This technique is known generally in the industry as rendering.
Previously, some methods were proposed to graphically specify the appearance of fine wrinkles and/or fine creases on objects for the rendering process. One method was to fully-mathematically define where the fine wrinkles and creases would appear on the object and fully physically simulating the three dimensional microscale geometry of the wrinkles. Another method was to dynamically adjust surface geometry based upon underlying object models, for example, skin on muscle models.
Drawbacks to these approaches for specifying fine wrinkles and creases included that the mathematical definition of such fine features for an object would require a large number of detailed surfaces that would be difficult to represent. Another drawback included that the simulation of the microscale geometry or performing a surface mapping based upon a underlying model would be computationally prohibitive. Yet another drawback was that if rendered, the specified features may not appear natural in the full and often extreme range of poses of the three-dimensional object.
Another method that was used to specify wrinkles included mapping of a two-dimensional image (texture maps) onto a three-dimensional object surface. Using these techniques, the wrinkles/creases are represented by a two-dimensional map, where the intensity of pixels in the map specify “peaks” and “valleys” of the surface. Another method, although not necessarily in the prior art, decomposed the texture map into directional-based texture maps. Next, at render time, the pose of the object is also decomposed into directional-based poses. Finally, the texture map is formed by combining the directional-based texture-maps and the directional-based poses.
Drawbacks to this approach for rendering wrinkles included that only one texture map would be used to specify wrinkles for all poses of the three-dimensional object. Similar to the technique described above, wrinkles that may appear natural in one character pose, may be inappropriate and unnatural looking in another character pose. For example, directional components often fade visually on and off in unnatural ways. Additional drawbacks include that the results are unintuitive and that the user cannot control the appearance and disappearance of wrinkles in arbitrary poses.
In light of the above, what is needed are improved techniques for users to specify wrinkles and creases for objects without the drawbacks described above.